Controlled relaxation of freshly drawn nylon



Oct. 10, 1961 G. PITZL 3,003,222

CONTROLLED RELAXATION OF FRESHLY DRAWN NYLON Filed Nov. 17, 1958 5114.1 Eig.2

' l6 J- B INVENTOR GILBERT PITZL BY W 21W ATTORNEY United States Patent 3,003,222 CONTROLLED RELAXATION 01F FRESHLY DRAWN NYLON Gilbert Pitzl, Chattanooga, Tenn., assignor to E. i. du Pont de Nemours and Company, Wiimington, Del., a corporation of Delaware Filed Nov. 17, 1958, Ser. No. 774,893 6 Claims. (Ci. 28-72) This invention relates to the process of drawing filaments of a synthetic linear polyamide, whereby orienta tion is produced along the longitudinal axis. More specifically, this invention relates to a process for improving the uniformity of such drawn product.

In the drawing of nylon yarn, it has long been customary to use as a windup, a spindle bearing a bobbin, and associated therewith a ring bearing a traveler which is traversed up and down the package. The customary package has a tapered or cigar-like shape, which is produced by varying the traversing stroke of the lay rail so that more yarn is wound near the center of the package than near the ends. Although this type of package has many advantages, such as stability, ease of manufacture, convenience in yarn take-ofl and the like, it has been discovered that certain yarn defects are produced therefrom.

When freshly drawn nylon yarn is wound onto a solid package, even at substantially zero tension, it is readily observed that the tension in the individual filaments gradually increases with time. When this eifect occurs in the multiple layers of yarn wound on a bobbin, tremendous compressive forces are developed. These forces act to compress the inner yarn layers; in response to these forces, the inner layers are crushed to some extent, and the filaments of which they are composed are free to retract. The filaments which are permitted to retract acquire a higher denier, lower modulus, higher break elongation, increased dyeability and lower relaxedshrinkage in boiling Water, as compared to the filaments which are restrained and cannot retract. There is, there fore, a difference in yarn properties radially throughout such a package. In addition, since each traverse stroke covers the ends and the center of the bobbin in a prescribed pattern, there is a diiference in properties of the yarn wound on the tapered ends of package, which yarn is not compressed and hence is not free to retract, and that wound near the center of the package, which yarn does retract due to the compression force of the yarn layers wound upon it.

It has been observed that when yarn from such tapered packages is woven into fabric, there occurs a fabric defeet which is known as pirn taper barre, which appears as a streakiness visible in both dyed and undyed fabric. The streakiness may be due to difference in dye depth, a denier variation, or variation in fabric construction which may be related to variable shrinkage in the warp, resulting in tight or loose warp ends. The frequency of these streaks has been found to correlate with the period of the traverse stroke.

A measurement of the shrinkage of yarn taken from such a tapered package, produced by exposure of a skein of yarn to boiling water, has shown that there is a significant dilference in shrinkage depending on the location in the package from which the yarn sample was taken. The frequency of this shrinkage variation has also been found to coincide with the streaks observed in woven fabric. The magnitude of the shrinkage variation has been shown to be proportional to the severity of the streaks. Therefore, in order to secure a more uniform yarn, the shrinkage differential throughout the package must be reduced.

It is known to reduce shrinkage by prior treatment of polyamide yarns or fabrics by steam or dry heat. A typical process is that described by Lewis in US. Patent 2,199,411. In this patent, a process is described for treating polyamide yarns with dry heat so that residual yarn shrinkage in boiling water is reduced from about 10% to less than 2%. It has now been discovered that yarn produced by this process has undesirable package properties. Packages of such yarn, when wound according to conventional procedures as indicated by Lewis, are not stable to shipping. There is too little tension in the yarn to prevent sloughing, and the yarn slips off the package, becomes tangled and useless. In addition, yarn treated according to Lewis may become so sensitive to small tension variations, such as those inherent in weaving, that additional streakiness is introduced because of those handling procedures.

It is, therefore, an object of this invention to provide a means for winding a nylon package from freshly drawn yarn, from which fabrics of a high degree of uniformity can be woven. It is a further object of this invention to provide a tapered package of nylon yarn which has a high degree of shrinkage uniformity throughout.

A further object of this invention is to provide a process for winding freshly drawn nylon yarn onto a package at such low tensions that the core can be made cheaply enough for a one-trip shipping package.

It is a still further object of this invention to provide a nylon package that has a high degree of stability toward shipment.

These and other objects are attained by an improvement in the drawing of polyamide strands wherein the freshly drawn strand is permitted a controlled relaxation of from about 7% to about 12% based on the length of the strand prior to relaxation, and is thereafter continuously wound to a package at a tension of from about 0.05 to about 0.35 grain per denier, in order to avoid substantial elongation of the strand on the package. By freshly drawn is meant that the strand is treated immediately subsequent to drawing, i.e., prior to packaging. By controlled relaxation is meant that the extent of relaxation is metered, e.g., by the relative peripheral speeds of advancing means, and that there results from such treatment a substantial reduction in both residual shrinkage and differential shrinkage throughout the strand package. This invention is applicable to yarns, filaments, and similar strands. The term yarn will be employed as exemplary of all such strands.

FIGURE 1 shows schematically an apparatus useful for attainng the objects of this invention.

FIGURE 2 illustrates the general contour of the yarn package wherein shrinkage variations occur.

FIGURE 3 shows a preferred arrangement of apparatus for accomplishing the relaxing step of this invention.

Referring to FIGURE 1, undrawn nylon yarn 1 is withdrawn from package 2, passed through pigtail guide 3, and then passed in multiple wraps about driven feed roll 4 and associated separator roll 5. From feed roll 4, the undrawn yarn it passes in several wraps about snubbing pin 6, as taught by Babcok in US. Patent 2,289,232. The yarn is drawn in frictional contact with pin 6 under the urging of draw roll 7 and its associated separator roll 8. Draw roll 7, of course, has a higher peripheral speed than feed roll 4, whereby the yarn is elongated to several times its original length. From draw roll 7, the yarn passes through heating unit 9 furnished with jacket 10 (heating means not shown), to relaxing roll 11 and its separator roll 12. The relaxation permitted the yarn is controlled by adjusting the relative peripheral speeds of rolls 1'1 and 7.

The yarn next passes through pigtail guide 13 and is wound onto a tapered twister package 16 by means of ring 14 and associated traveler 15. The tension in the yarn wound to package 16 is controlled by the weight of traveler 15, as is well known in the art.

An essential feature of the process of this invention is to provide a controlled amount of relaxation of the freshly drawn yarn. This relaxation can be provided by the apparatus described hereinabove, when draw roll 7 and relaxing roll 11 are run at predetermined different peripheral speeds. However, suitable conditions must exist in order for the yarn to retract the required amount during the time it takes for said yarn to pass from roll 7 to roll 11. This relaxation will occur at ordinary (room) temperatures and humidities if sufficient time is allowed in going from 7 to 11. However, at present-day processing speeds, an unduly large distance would be required in order to give the yarn time to relax sufiiciently. Therefore, in accordance with a preferred embodiment of this invention, relaxation is accelerated by exposing the yarn to elevated temperatures in the presence of moisture in the form of steam. This is accomplished, as described hereinabove, while the yarn passes through heating unit 9. Heating unit 9 may suitably be furnished with a small opening for the yarn to enter and another small opening for exit, to retain as much steam therein as possible. A heating or insulating jacket 10 may be furnished, if desired, to prevent undue condensation of the steam.

Dry heat may likewise serve to accelerate relaxation of the yarn. Under these conditions, tube 9 is heated to a high temperature, and the heat is transferred to the yarn by means of radiation and convection. Alternatively, heat may be supplied to the yarn by contact with one or more hot plates.

The tension at which the yarn is wound onto package 16 may be controlled by the weight of traveler as is well known in the art of ring twisting. In accordance with this invention, it is important that winding tensions be controlled between about 0.06 and about 0.35 gram per denier to reduce the shrinkage level of the packaged yarn and also the shrinkage variation within the package. Shrinkage level of a yarn package is the average residual shrinkage of all yarn in the package. Excessively low tensions result in unstable packages which are not suitable for shipping, and higher tensions such as are introduced by heavy travelers decrease the advantages obtained by the controlled relaxation step. Yarn wound under such high tensions has a high and nonuniform shrinkage throughout the package.

The following examples illustrate specific embodiments of this invention.

EXAMPLE I Polyhexamethylene adipamide yarn of 34 filaments and 208 (spun) denier is drawn in an apparatus arrangement substantially as shown in FIGURE 1, to a final denier of 70. Samples of this drawn yarn are then subjected to a series of relaxation treatments, using the apparatus of FlGURE l, as described below in relation to Table I. Steam is supplied to the oven 9 at 100 C. Drawn yarn speed through the oven is 562 yards per minute, and the oven is 12 inches long. Contact time between steam and yarn is, therefore 0.03 second. Winding tension in this series of tests is controlled at 0.17 g.p.d.

Table I shows the improvement in yarn shrinkage level and shrinkage uniformity as the extent of yarn relaxation is changed.

Table I Percent Shrinkage Percent Steam Test Relaxation temp, Through Bobbin 0. Outsideavg.

Range 2 MTBD 3 none none 9. 1 1. 71 1. 67 uncontrolled" 7. 5 1.96 1.03 5 5 none 9. 5 1. 48 1.32 100 7. 2 0. 92 0. 86 100 6.7 1.02 0.80 100 6.1 0.85 0. 79

100 yarn breaks down 1 Outsideavg. is average residual shrinkage of yarns at the surface of the package.

2 Shrinkage range is maximum dilIerence in shrinkage between samples taken from the same bobbin.

3 M D is maximum taper-to-barrel difierentlal in yarn residual shrinkage.

After relaxing the yarn samples under the conditions shown in Table '1, packages of each sample are held 7 days at 75 F., 72% relative humidity, prior to testing. The yarn samples are obtained by stripping yarn from the double taper package shown in FIGURE 2 until the middle or a barrel portion is reached (B, FIGURE 2). A sample -150 cm. long is then removed and immediately measured, as described hereinbelow. The stripping process is continued until the extreme taper portion of the bobbin is reached (position A or C, FIGURE 2), and another sample of 130-150 cm. is taken. The stripping is continued, taking samples from the extremities of the package and from the longitudinal center of the bobbin, all the way through the bobbin.

Sample length is determined immediately after removal; the ends of the yarn segment are knotted together, a weight of 0.1 g.p.d. is hung in the loop, and the length of this loop is then measured. After determining the initial length, the loop of yarn is submerged in boiling water for a period of 20 minutes, after which it is removed and dried for a total of about 25 minutes, under tension at 0.1 g.p.d. The length of the boiled-off loop is again measured and the percent shrinkage is calculated, based on the length of the original sample.

Test AA shows typical values for conventional drawing process, without provision for relaxation and without use of heating oven. The average shrinkage level of yarn processed under these conditions is 9.1%, with an average range of 1.71% through the bobbin. Under the conditions of test AA, of course, the yarn by-passes rolls 11, 12.

Test AB represents the same conditions as test AA, except that steam at 100 C. is introduced into oven 9. The yarn is thus permitted to relax as much as possible under the established winding tension of 0.17 g.p.d., but the amount of relaxation is not predetermined by means of rolls 11, 12. Under these conditions, the average shrinkage is 7.5%, but there is an even greater shrinkage spread (1.96%) than was the case with conventional drawing (test AA).

Test AC represents conditions in which a 5.5% relaxation is obtained by the use of rolls 11, 12., adjusted to turn at a peripheral speed of 0.945 times that of rolls 7, 8. In this test, no steam is admitted to oven 9, which remains unheated. The 5 5% relaxation represents that relaxation which is obtained while the yarn travels from roll 7 to roll 11, a distance of 2 feet. The time available for relaxation, at 75 F, 78% R.H., is 0.08 second. It is apparent that there is little if any difference between the shrinkage level and shrinkage uniformity of this yarn and that of test AA representing conventional drawing.

Test conditions AD, AE, and AF show the advantages obtained with controlled amounts of relaxation, using 100 C. steam in oven 9. It is apparent that a significant degree of improvement in shrinkage level and shrinkage uniformity is obtained. When the relaxation is increased from 10.5%, to 12% at 100 C. steam temperature, the

yarn does not relax enough and the threadline breaks down, due to its backwrapping on draw roll 7. A comparison of the properties of yarn AD with those of yarn AB demonstrates the efiicacy of controlled relaxation. Both yarns have been relaxed to about the same extent, insofar as the extent of relaxation may be inferred from the average residual shrinkage of the latter yarn, yet both the shrinkage range and the taper-to-barrel differential shrinkage of yarn AD are substantially improved over that of yarn AB, a yarn which is representative of those produ-ced in accordance with prior art procedures.

When fabrics are woven with yarns AA, AB, and AF in the filling, AA and AB show a severe streakiness or pirn taper barr; fabric AF is acceptable, with only a very faint indication of barr.

EXAMPLE II Percent Shrinkage Test Through Bobbin Outsideavg.

Range MTBD BA" BB BO Table II shows that increasing the temperature of the steam improves shrinkage uniformity, although there is little elfect on the average shrinkage level. Such improvements in shrinkage uniformity represents a significant improvement in fabric quality. When woven into fabrics, the samples are rated as indicated in Table III.

Table II Test Yarn Appearance of Fabric Prepared From Yarn Very faint pirn taper barremild improvement in warp streaks over conventional fabrics. No pirn taper barrconsiderable improvement in warp strnks over conventional fabrics.

EXAMPLE I1 1 The effect of winding tension on yarn shrinkage at a constant temperature of 175 C. and a constant relaxation of 10.5% is shown in Table IV. The procedure of test AF in Example I is followed.

6 EXAMPLE IV The process of this invention may be carried out in the absence of steam (-i.e., using dry heat), by subjecting the yarn to higher temperatures. This procedure is illustrated by this example.

Yarn is drawn following the procedure of test AB in Example I. In this case, however, no steam is admitted to oven 9; the oven is heated by means of electrical heaters embedded in the jacket 10. The yarn is thus subjected to radiant heat from the walls of the oven. A thermocouple placed within the oven, prior to introduction of the yarn, registers an air temperature of 450-550" C. The oven tube in this case is 12 inches long, so that the yarn is exposed for 0.03 second in the heated tube. Relaxing rolls 11, 12 are set to permit 9% relaxation. Properties of yarn produced at two different winding tension levels are shown in Table V.

Table V indicates that a satisfactory degree of reduction in shrinkage and shrinkage variation through the bobbin is obtained using dry heat. The improvement previously noted when winding tensions are decreased is observed here also. When the tensions are lowered below about 0.06 g.p.d., poor package formation is noted.

EXAMPLE V This example illustrates the improvement in shrinkage and shrinkage uniformity obtainable when the yarn is relaxed a controlled amount at room temperature. This may be accomplished at conventional drawing speeds by increasing the length of yarn path between roll 7 and roll 11 of FIGURE 1.

The test procedure of Example I, test AC is repeated, except that in this case a relaxation of 8.5% is employed. The yarn path between rolls 7 and 11 is increased to 12 feet, and oven 9 is by-passed. The drawing speed is 500 yards per minute (y.p.m.), hence the yarn remains in the relaxing zone (between rolls 7 and 11) for 0.48 second. When wound onto a package at a tension of 0.09 g.p.d., approximately reduction in yarn property variation throughout the package is observed.

EXAMPLE VI This example illustrates the effect of yarn denier and extent of drawing on the upper limit of relaxation. All yarns are composed of polyhexamethylene adipamide, are relaxed 12%, and thereafter packaged at about 0.09 g.p.d. tension using the apparatus of Example I, the steam Table IV 0 temperature being 175 C. throughout the test series.

Table VI Percent Shrinkage Tension Final Denier Comments Test (g.p.d.) Through Bobbin Outside avg.

TBD 30 (10 filaments) good operability. Range M 40 (13 fi1aments) c Do. go 1130. .l .66 0.34 0 o. 8. 6 24 0. 24 (3A1 filaments)... go. h k O o. 0- 0 y sloug 8 off p age do yam breaks down.

Table IV shows that a significant improvement in shrinkage level and shrinkage uniformity is obtained as winding tension is decreased. However, when the wind- Table VI indicates that satisfactory operability can be obtained at 12% relaxation for a number of yarn counts. Under the above conditions, however, the yarns break down or the threadline action becomes erratic at 13% EXAMPLE VII This example shows the effect of controlled relaxation on percentage residual shrinkage at the upper limits of relaxation. The following tests are carried out using the apparatus of Example I with S denier, 17 filament polyhexamethylene adipamide yarn. The steam temperature is 175 C. and the yarn tension is about 0.05 g.p.d. throughout this series.

Table VII Percent Percent Test Relaxation Shrinkage,

Average In these tests, operability of FD and FE is marginal, owing to borderline relaxing tension. In fact, the operability of tests FD and FE is probably not sufficient for a practical process. These results are characteristic of controlled relaxation, i.e., no additional reduction in residual shrinkage is attained by increasing the amount of relaxation beyond the upper limit of this invention. These results differ from prior art procedures involving preshrinkage, setting, and various other phenomena; in such cases residual shrinkage usually is linearly related to the amount of lengthwise retraction, reductions therein being achieved without appreciable improvement in differential shrinkage properties.

In the practice of the present invention, steam is a preferred agent for accelerating the relaxation of the freshly drawn polyamide yarn, due to its effectiveness, cheapness and safety. Using steam, relaxation occurs most rapidly for a given temperature of exposure, thus permitting use of a small treating oven and conserving machine space. Saturated steam is effective, but superheated steam is preferred. Steam temperatures of from 100250 C. and above are satisfactory for polyamides, and even higher steam temperatures are possible if the polyamide is not low-melting or susceptible to degradation. Due to the short contact time, steam temperatures higher than the polymer melting point may be employed. The preferred steam temperature range is from about 140 C. to about 180 C. as permitting operations with a minimum of difficulties.

As has been described hereinabove, the length of the steam treating oven will depend on the temperature of the steam and on the drawing rate of the yarn. Thus, for high speed drawing a longer oven will be needed at a given steam temperature; conversely, higher steam temperatures may be used when it is desired to cut down on the oven length. At drawing speeds of 562 y.p.m., an exposure time of 0.03 second is satisfactory when using 150 C. steam for treatment. For these conditions, therefore, an oven length of 12 inches is satisfactory.

It is also within the scope of this invention to induce yarn relaxation by wetting the yarn and then passing it through an oven or over a hot plate at temperatures of 100 C. or higher.

Other agents have lesser utility in promoting the relaxation step; among such reagents are the mild swelling agents disclosed in U.S. Patent 2,157,119. A useful class of these reagents is hydroxylated non-solvents for nylon, such as methanol, ethanol, and the like.

This invention also includes the use of dry heat to induce the relaxation step. In general, higher oven temperatures will be required than when steam is used; or, conversely, a longer exposure time will be needed. The dry heat treatment may be carried out in the presence of air, although excessively severe treatments (in length of exposure or high temperature) must be avoided. Due to the high surface temperatures required to provide sufiicient heat transfer to the yarn by radiation, the yarn must be protected from accidental contact with these high tem perature surfaces. Alternatively, lower temperature surfaces may serve to heat the yarn by contact; flat or curved plates (grooved or of other contour), heated tubes, and the like may be used to supply heat to the yarn. Alternatively, the yarn may pass through high temperature liquid baths, provided such are inert toward the yarn; mineral oil, molten metal, or the like may be used in such baths.

It has also been shown that the relaxing step of this invention may be carried out at room temperatures by decreasing yarn drawing speeds, or by increasing the time of travel for the yarn between draw roll and relaxing roll. Such alternatives are usually undesirable, since they result in a decrease in machine productivity or a costly increase in machine size.

The process of this invention has been illustrated (FIGURE 1) by reference to an apparatus wherein separate draw and relaxing rolls are employed. However, a more compact and economical apparatus arrangement 7 for accomplishing the relaxing step is shown in FIGURE 3. In this arrangement, draw roll 23 is of stepped construction, having a portion of larger diameter, indicated at 7, and a portion 17 of smaller diameter. Idler-separator roll 8 is employed as in FIGURE 1, but two supplemental separator rolls 18, 19 are added. The steam tube or oven is shown at 9, furnished with steam inlet connection 20, condensate trap 31, and condensate return 22.

In operation, yarn 1, drawn in snubbing contact with pin 6, passes in multiple wraps about the large diameter part of draw roll 23 and separator roll 8, as in FIGURE 1. The yarn then traverses steam oven 9, changes direction over idler roll 18, and passes in multiple wraps over the smaller diameter portion 17 of draw roll 23 and separator roll 19. The relaxed yarn, guided by pigtail 13, is then wound up as shown in FIGURE 1.

The controlled relaxation step of this arrangement (FIGURE 3) is obtained because the peripheral speed of the two portions 7 and 17 of the draw roll differ in pro portion to their diameters; once the required degree of relaxation is determined, a suitable draw roll of stepped diameters can be fabricated. This arrangement prevents variation in the degree of relaxation, avoids expensive machine drives or gear linkages, and permits a very compact arrangement.

Winding tensions satisfactory for the process of this invention are between about 0.06 to about 0.35 g.p.d., with a preferred range of from 0.1 to 0.25 g.p.d. Such tensions are conveniently obtained by use of the proper size traveler on the twister ring, considering also the denier of the yarn being wound, as is well known to those skilled in the art. In this connection, it has been observed that a winding tension of about 2 grams absolute represents the least tension which can be used in a practical process for winding low-denier yarns. Alternatively, suitable tension devices may be used for other types of traversing and winding mechanisms. It is essential to maintain winding tension high enough to prevent sloughing of the package during shipment, but low enough to prevent objectionable retensioning of the yarn. In general, under otherwise the same processing conditions, lower levels of yarn tension permit a proportionately greater improvement in residual shrinkage and shrinkage uniformity, both being achieved with improved operability up to the upper limits of relaxation of this invention.

The process of this invention has been described in terms of winding an improved double-tapered package on a ring twister windup, but it may be advantageously employed for spindle-wound packages of other shapes such as bottle bobbins, filling wind bobbins, headed spools, and the like. At high relaxations, it is often preferred to used a ring-traveler windup because of the low and uniform tension at which the yarn is wound onto the package. Similarly, the use of the til-ling wind permits similar uniformity of yarn take-oft tension. In addition, it is advantageous to use the process of this invention in winding squareor tapered shouldered packages upon cylindrical bobbins using conventional reciprocating traverses (in which no twist is inserted), thereby decreasing shrinkage differences between yarn on the inside and the outside of such packages. This improvement is obtained by applying a suitable tension to the yarn prior to winding. This invention makes it possible to wind freshly drawn polyamicle yarn on paper (cardboard) cores, thus providing a single-use or one-Way shipping package in one operation. This has been impossible heretofore, since the retractive forces of the freshly drawn yarn are sufficient to crush low-cost cardboard tubes or cones; a repackaging operation has always been necessary. After packaging, there is observed a gradual improvement in the level of residual shrinkage in yarns treated in accordance with this invention. Such improvement becomes negligible after about 30-days storage.

The yarn counts for which this invention is useful may range from monofilament yarns to any desired number of filaments; for heavy denier yarns, it may sometimes be necessary to increase the heating time or temperature in the oven to compensate for the greater mass of the filament bundle. In particular, the upper limit of relaxation has been observed to depend on the denier of the yarn being relaxed and on the extent to which it has been drawn.

The process of this invention is especially useful for synthetic linear polyamides; by synthetic linear polya-mides is meant those disclosed, for example, by Carothers in US. Patents 2,071,250 and 2,071,253. The preparation and spinning of such polyamides is disclosed in US. Patents 2,130,948; 2,163,636; and 2,477,156. Examples of such polyamides are those prepared from suitable diarnines and suitable dicarboxylic acids, such as hexamethylene diamine and adipic acid. Similarly, polyamides from omega aminocarboxylic acids or their amide- 10 forming derivatives, e.g., polyamide from caprolactanfl, are included. v

This application is a continuation-in-part of application Serial No. 661,095, filed May 23, 1957, by Gilbert Pitzl, and now abandoned.

The claimed invention:

'1. A process comprising elongating a substantially undra'wn polyamide yarn to several times its initial length followed immediately by relaxing the yarn in an amount between about 7% and about 12%, based on the length of the elongated yarn prior to relaxation, and then winding the relaxed yarn into a stable package at a tension low enough to avoid substantial elongation of the yarn during winding on the package.

2. The process of claim 1 in which the polyamide is polyhexamethylene adipamide.

3. A process comprising elongating a substantially undrawn polyamide yarn to several times its initial length followed immediately by relaxing the yarn in an amount between about 7% and about 12%, based on the length of the elongated yarn prior to relaxation, and then winding the relaxed yarn into a stable package at a tension between about 0.06 and about 0.35 gram per denier.

4. The process of claim 3 in which the yarn is relaxed in the presence of steam.

5. The process of claim 4 in which the steam temperature is between about and about C., and the relaxed yarn is wound into a package at a tension between about 0.1 and about 0.25 gram per denier.

6. A process comprising elongating a substantially undrawn polyhexamethylene adipamide yarn to several times its initial length followed immediately by relaxing the yarn in the presence of steam at a temperature between about 140 and about 180 C. in an amount between about 7% and about 12%, based on the length of the elongated yarn prior to relaxation, and then winding the relaxed yarn into a package at a tension between about 0.1 and about 0.25 gram per denier.

References Cited in the file of this patent UNITED STATES PATENTS 1,867,617 Elssner July 19, 1932 2,289,232 Babcock July 7, 1942 2,584,779 Averns et a1 Feb. 5, 1952 2,664,009 Emerson Dec. 29, 1953 2,807,863 Schenker Oct. 1, 1957 2,956,330 Pitzl Oct. 18, 1960 

1. A PROCESS COMPRISING ELONGATING A SUBSTANTIALLY UNDRAWN POLYAMIDE YARN TO SEVERAL TIMES ITS INITIAL LENGTH FOLLOWED IMMEDIATELY BY RELAXING THE YARN IN AN AMOUNT BETWEEN ABOUT 7% AND ABOUT 12%, BASED ON THE LENGTH OF THE ELONGATED YARN PRIOR TO RELAXATION, AND THEN WINDING THE RELAXED YARN INTO A STABLE PACKAGE AT A TENSION LOW ENOUGH TO AVOID SUBSTANTIAL ELONGATION OF THE YARN DURING WINDING ON THE PACKAGE. 